1. Field of the Invention
This invention relates to a method for removing micro-bubble and/or particles from a liquid and a liquid supply apparatus utilizing the method, and more particularly to a method of utilizing laser to remove micro-bubble and/or particles from a liquid, a liquid supply apparatus utilizing the method, and an immersion exposure apparatus that incorporates the liquid supply apparatus.
2. Description of the Prior Art
Liquid is used in many industries as a medium for reaction or measurement, etc. However, micro-bubbles and/or particles in a liquid frequently cause problems.
Taking the semiconductor industry as an example, a liquid like water is used in the immersion lithography that is recently developed for the following reasons. As the linewidth of semiconductor process is to be reduced, the most direct way is to reduce the wavelength of the exposure light and thereby enhance the resolution. However, there are so many issues to be solved, such as the laser source, photomask material, lens material and photoresist material, for the new-generation lithography process of 157 nm. For example, it is difficult to fabricate lenses of calcium fluoride suitable for 157 nm exposure, for the lenses either have many defects or cause significant aberrations and thus cannot project a clear image on the wafer. Hence, the immersion lithography is developed, which allows the resolution to be enhanced based on current 193 nm lithography instead of the development of 157 nm lithography. The immersion lithography method is to inject water between the light source and the wafer in a 193 nm exposure system to reduce the wavelength to 132 nm, so that 65 nm, 45 nm and even 32 nm processes can be supported by the immersion lithography instead of current dry lithography systems.
However, there are still some technical problems in immersion lithography. For example, the exposure light may be scattered by the micro-bubbles or particles in the water in the immersion exposure system so that many defects are incurred in the image transferred to the wafer.